Optionally send optional values

[marccampbell]

only send embeddedClusterDownloadEnabled and embeddedClustermultinodeenabled when they are set. this avoid the following error:

ERROR: 400
METHOD: POST
ENDPOINT: https://api.replicated.com/vendor/v3/customer
is_embedded_cluster_multinode_enabled cannot be true if is_embedded_cluster_download_enabled is false

The problem is that embeddedClusterDownloadEnabled is true in the license policy, but the current CLI is sending false if i don't specify it.